1. Field of the Invention
The invention relates generally to tire treads having voids within a thickness of the tire tread, and, more specifically, to treads having features for restricting the flow of material into such voids during tire molding and/or curing operations, and/or reducing crack initiation and/or propagation along any such void during tire operation.
2. Description of the Related Art
It is commonly known for tire treads to contain various molded tread elements and features to enhance tire performance. It is also commonly known that these molded tread elements and features may be formed concurrently with a tire during tire molding and curing operations, or independently by way of a tread mold prior to applying the tread to a tire or tire carcass, such as when performing tire retreading operations.
Tread features include, without limitation, grooves and sipes, each of which form voids within a thickness of the tread. In certain instances, the tread voids are maintained below an outer tread surface, or, in other words, submerged (i.e., hidden or embedded) below the outer tread surface in such a way as to be substantially hidden from view in the new state of the tread. In such instances, submerged features may be provided to supply additional tread void and/or traction edges for enhanced tire performance at worn stages of the tire tread. When a tread is pre-formed, such as for retreading a tire, the submerged tread voids may be formed along or through the underside surface of the tread, the underside surface being the surface that will later be bonded to the tire casing. Accordingly, the void is open to the tread underside surface. After the tread is formed, it is applied to a tire or tire carcass.
After a pre-molded tread is applied to a tire, the tire is finally molded or cured in a subsequent process, where the tire is heated and pressurized. During any such process, uncured material, such as bonding material, may be forced into the void through the underside surface. In effect, this material at least partially fills the void, which may reduce the effectiveness of the submerged feature. For example, when the feature is a groove, the groove provides a void to consume or absorb water for improved wet performance. When the groove, however, is at least partially filled with the displaced material, the void volume and the effectiveness of the groove is less than optimal. In another example, the tread feature may comprise a sipe, which generally comprises a slit or narrow groove. The sipe provides an additional traction edge for improved tire traction, but also has the effect of reducing local tread stiffness due to the discontinuity that it forms. When the sipe, however, becomes at least partially filled with displaced material, the sipe may operate less than optimally as a traction edge, and/or to reduce the local stiffness of the tread. Accordingly, there is a need to substantially limit and/or prevent the influx, flow, or entry of material into a tread feature void from the underside of the tread during a curing operation.
A further problem may arise during tire operation, subsequent to tire formation. More specifically, when a void extends to the underside of a tread, a crack may initiate in proximity to the void, such as where the void intersects the tread underside surface.